2,600 letters have been recovered in a postmaster’s trunk, containing extensive historical and cultural evidence from 17th-century Europe, BBC History Magazine has revealed. 600 of them are still sealed shut, and will be read for the first time using the latest advances in x-ray technology.

The trunk contains 2,600 letters sent from France, Spain and the Spanish Netherlands between 1689 and 1706 but never delivered – including 600 letters never opened – because their recipients could not be found or would not pay outstanding postage costs. The trunk has been stored in The Hague’s Museum voor Communicatie since 1926. An international team of experts from MIT, Yale University, and the Universities of Leiden, Groningen, and Oxford is exploring them to find out more in a ground-breaking project called Signed, Sealed, & Undelivered.

Collected by the postmasters of the Dutch city of The Hague – Simon de Brienne and his wife Maria Germain – the letter-writers come from all levels of society, from aristocrats to wandering musicians, women as well as men, each with their own stories to tell. Beyond its written information, the trunk is a valuable physical resource, from the wax seals on its seal-skin-covered exterior to the ways the letters were folded.

Dr Daniel Starza Smith, from Lincoln College, University of Oxford notes: “How a letter was folded can express personality and period just as handwriting can." Jana Dambrogio, conservator at MIT Libraries, adds: “But the inventiveness and complexity here is like nothing we have ever seen. It allows us to study what we call ‘letterlocking’: the tradition of folding and securing a writing surface to function as its own envelope. This is an entirely new area of study, so the trunk offers us amazing research opportunities.”

For further information, please visit: www.brienne.org. The team is tweeting with the hashtag #SignedSealedUndelivered; or follow @letterlocking.